The present invention relates to an electronic component for high frequency power amplification, and particularly to a technology effective when applied to an electronic component for high frequency power amplification, which needs power-up characteristics at the start of transmission with a GSM cellular phone or the like as a representative.
A high frequency power amplifying electronic component (hereinafter called “RF power amplifier module”) equipped with a high power amplifier (HPA) with transistors such as a MOSFET (Metal Oxide Semiconductor Field-Effect-Transistor), a GaAs-MESFET, etc. as amplifying elements has been built in a transmission section of a wireless communication apparatus such as a cellular phone or the like. In general, a system is configured in a cellular phone in such a manner that the cellular phone performs call processing while changing output power (transmission power) so as to adapt to ambient environments in accordance with power level indication information sent from a base station, and does not cause interference with other cellular phones. In a cellular phone of a GSM (Global System for Mobile Communication), for example, an APC (Automatic Power Control) circuit is mounted in an RF power amplifier module. The APC circuit compares a detected signal of an output signal and an output level indication signal Vramp sent from a baseband circuit and controls transmission power by control on the gain of each amplifying stage. Regarding such an RF power amplifier module, the following technologies have been known.
A high power amplifier in which a bias control voltage Vapc for defining transmission power is applied to respective gates of power amplifying MOS transistors coupled in tandem in three stages, via resistance division has been shown in, for example, FIG. 2 of a patent document 1 (Japanese Unexamined Patent Publication No. 2005-197859). The high power amplifier is further provided with a MOS transistor (Q1) having the same structure as the power amplifying MOS transistor and has the function of converting a current flowing through the MOS transistor (Q1) to its corresponding voltage by a resistor (R6) and reflecting it on the bias control voltage Vapc. According to this, since the manufacturing variations in the threshold voltage of the power amplifying MOS transistor are monitored by the MOS transistor (Q1) and reflected on the bias control voltage Vapc, variations in bias current of the power amplifying MOS transistor can be compensated.
An electronic component for high frequency power amplification in which a bias current corresponding to a bias control voltage Vapc for defining transmission power is supplied to an amplifying transistor (Qa3) via a current mirror circuit (Qa3, Qb3), has been shown in, for example, FIG. 3 of a patent document 2 (Japanese Unexamined Patent Publication No. 2006-238244). The electronic component is further provided with a precharge function that a bias current set to a fixed value is supplied to the amplifying transistor (Qa3) at low power with the rise of power. Described specifically, the current (current corresponding to the bias control voltage Vapc) flowing through the amplifying transistor (Qa3) is detected by a current detector 224, and its voltage-converted value and a reference voltage Vpre are compared with each other. When the voltage-converted value is small, the bias control voltage Vapc is raised via a transistor (Qe). On the other hand, when the voltage-converted value is large, the transistor Qe is turned off so that a bias control voltage Vapc is generated according to an output level indication signal Vramp and a detected signal (Vdet) sent from a power detector (221). According to this, the precharge function can be realized by hardware and an improvement in spectrum characteristics with the rise of power can easily be realized.